1. Field of the Invention
The present invention relates to an image reading apparatus, an image reading method and a computer-readable information recording medium, and, in detail, to an image reading apparatus, an image reading method and a computer-readable information recording medium, for reading an image of an original with appropriately adjusting an image reading speed at low cost.
2. Description of the Related Art
In an image reading apparatus of a scanner apparatus, a copying apparatus, a facsimile apparatus, a multifunction peripheral apparatus or such, in a case where an original reading unit that does not move reads an image of an original while the original is conveyed by an automatic document feeding unit, a photoelectric conversion device such as a CCD (charge coupled device) or such of the original reading unit converts reflected light from the original to read the image data of the original, main scan line by main scan line. The image data of the original are then temporarily stored in a memory having a predetermined capacity, and then, the image data of the original are transferred from the memory to an image processing unit that carries out various sorts of image processing on the image data and produces an output image.
The image reading apparatus continuously carries out in sequence a series of operations of once storing the image data read by the original reading unit, and then transferring the stored image data to the image processing unit that then carries out image processing on the image data. Ordinarily, an image data reading speed of the original reading unit (i.e., an image data storing speed for transferring the image data to the memory and storing the image data in the memory) is set higher than an image processing speed of the image processing unit (i.e., an image data transferring speed for transferring the image data from the memory to the image processing unit). Therefore, along with a progress of the image reading operation, an image data stored amount in the memory increases accordingly. Since the memory has a limited capacity, the image data transferred to the memory from the original reading unit may not be stored in the memory and may be lost when the data amount stored in the memory exceeds the storage capacity of the memory.
Then, in the image reading apparatus, scanning and reading of image data by the original reading unit is interrupted when the data amount of image data stored in the memory becomes close to the storage capacity of the memory, and transferring the image data to the memory is interrupted, while transferring the image data to the image processing unit from the memory is continued. Thereby, the data amount of the image data stored in the memory is reduced accordingly. Then, the image reading apparatus re-starts scanning and reading of image data by the original reading unit when the data stored amount in the memory has been reduced to a predetermined data amount, and transferring of the image data to the memory from the original reading unit is also re-started. Thus, so-called intermittent reading operation is carried out in which operation of the original reading unit is interrupted and re-started appropriately as mentioned above.
In the image reading apparatus, in a case where the original conveyance is carried out by an ADF (Auto Document Feeder), the intermittent reading operation is carried out in such a manner described below. That is, the image reading apparatus provided with the ADF drives a feeding roller or such by means of a driving motor (for example, a stepping motor), plural sheets of an original set on a original table are conveyed to the original reading unit sheet by sheet, the original reading unit reads image data of the original, and image data of the original thus read are transferred to the memory. Then, when the data amount of the image data thus stored in the memory becomes close to the storage capacity of the memory, a rotational speed of the driving motor that drives the ADF is reduced, and finally, the driving motor is stopped. Thus, a speed of feeding the original is reduced to a speed lower than that of an ordinary reading operation, and finally, the ADF is stopped. Such an operation is referred to as “slow-down reading operation”, hereinafter. After that, in the image reading apparatus, the image data stored in the memory are transferred to the image processing unit in sequence. Then, when the data amount of the image data stored in the memory has been reduced to the predetermined data amount, the once stopped driving motor is again driven, first at a speed lower than that of the ordinary reading operation, the rotational speed of the driving motor is increased to the rotational speed of the ordinary reading operation. The original is thus conveyed at an original conveyance speed in the ordinary reading operation. Such an operation is referred to as “slow-up reading operation”, hereinafter. That is, in the image reading apparatus in the related art, the slow-up reading operation and the slow-down reading operation are simply repeated, scanning and reading is thus stopped and re-started, and thus, intermittent reading operation in a simple stop/start way is carried out.
Further, in the image reading apparatus in the related art, generally speaking, an inexpensive stepping motor that merely requires a simple control mechanism is used as the driving motor.
Further, in the related art, driving control clock pulses used for driving the stepping motor that conveys a sheet of an original are counted, plural driving patterns are prepared for controlling driving states of the stepping motor in response to load states of the stepping motor according to a position at which the sheet of the original is conveyed. Then, when conveyance of the original is stopped and re-started in reading image data of the original, a driving pattern is selected corresponding to a load state of the stepping motor concerning a position at which the original is stopped according to the counted number of the pulses, and a driving state of the driving motor is controlled according to the selected driving pattern (see Japanese Laid-Open Patent Application NO. 10-145551).
That is, in the related art, upon the intermittent reading operation in which an image data reading operation is stopped and re-started, a load fluctuation of the stepping motor is obtained, a driving pattern according to a load state is selected, and driving of the stepping motor is controlled according to the selected driving pattern. Thus, even when an original conveyance path has a large load fluctuation or even in the intermittent reading operation during an image data high-speed reading operation, an occurrence of a distortion in read image data or a synchronization loss is avoided.
In the above-mentioned intermittent reading operation, image data read by the original reading unit during the slow-up/slow-down reading operation have an increased resolution as a reading speed is decreased. Therefore, when image data of the entirety of the original are restored from the read image data by the image processing unit, image processing may be carried out in such a manner that an operation of thinning out image data in units of main scan lines on the image data read by the original reading unit may be carried out, depending on whether the image data were read in the slow-up/slow-down reading operation or the ordinary reading operation. Thus, finally, image data of the original may be appropriately restored.